US 8052069 B2
The present invention comprises a high performance, vertical, zero-net mass-flux, synthetic jet actuator for active control of viscous, separated flow on subsonic and supersonic vehicles. The present invention is a vertical piezoelectric hybrid zero-net mass-flux actuator, in which all the walls of the chamber are electrically controlled synergistically to reduce or enlarge the volume of the synthetic jet actuator chamber in three dimensions simultaneously and to reduce or enlarge the diameter of orifice of the synthetic jet actuator simultaneously with the reduction or enlargement of the volume of the chamber. The jet velocity and mass flow rate for the present invention will be several times higher than conventional piezoelectric synthetic jet actuators.
1. A synthetic jet actuator comprising:
an electroactive cylindrical wall;
a first end electroactive diaphragm; and
a second end electroactive diaphragm;
wherein the first and second end electroactive diaphragms are joined to the electroactive cylindrical wall at opposing ends of the electroactive cylindrical wall such that the formed chamber has a closed cylinder shape; and wherein the electroactive cylindrical wall defines an orifice therethrough; and further wherein a positive strain and a negative strain of the electroactive cylindrical wall are configured such that, when voltage is applied to the electroactive cylindrical wall, (i) a height of the electroactive cylindrical wall decreases, (ii) a thickness of the electroactive cylindrical wall increases, (iii) an inner diameter of the electroactive cylindrical wall decreases, and (iv) a diameter of the orifice decreases.
2. The synthetic jet actuator of
3. The synthetic jet actuator of
4. The synthetic jet actuator of
5. The synthetic jet actuator of
6. The synthetic jet actuator of
7. The synthetic jet actuator of
wherein the decrease of the inner diameter of the electroactive cylindrical wall further enhances the flexing of the first and second end electroactive diaphragms toward each other.
8. The synthetic jet actuator of
This application is related to U.S. application Ser. No. 12/354,808, filed Jan. 16, 2009, which in turn claims priority to U.S. Provisional Application No. 61/091,510, filed Aug. 25, 2008; and U.S. application Ser. No. 12/355,782, filed Jan. 18, 2009, which in turn claims priority to U.S. Provisional Application No. 61/091,512, filed Aug. 25, 2008, the contents of which are incorporated herein in their entirety.
The invention was made in part by employees of the United States Government and may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
The present invention relates generally to synthetic jet actuators and, more particularly, relates to synthetic jet actuators with multiple electroactive components.
Active flow control changes the paradigm of aerodynamic design of current and future wing-borne systems in subsonic, transonic and supersonic flow. Active flow control should be an inherent input to the conceptual design of the next generation of commercial and military flight vehicles. Retrofitted to current fixed-wing aircraft, active flow control can “clean up” complex three-dimensional, external flow separations on the wing top surface particularly severe under maneuvering conditions. Active flow control can inhibit flow distortion at the compressor face in supersonic inlets emanating from shock/boundary-layer interactions on the inlet sidewalls, at the inlet throat, and in the subsonic diffuser. Active flow control makes feasible aerodynamic design for high lift/drag ratios at cruise and efficient subsonic/transonic performance at off-design conditions, taking into account environmental and performance constraints. The outcome is a reduction in overall drag of the vehicle, alleviation of unsteady loads and prevention of the expulsion of the inlet shock system (that may lead to catastrophic loss of the airframe).
It is known to use a synthetic jet (also termed a zero net mass flux jet) to influence the flow over a surface, for example to control flow separation from an airfoil. An isolated synthetic jet is produced by the interactions of a train of vortices that are typically formed by alternating momentary ejection and suction of fluid through an orifice of an actuator. A typical synthetic jet actuator (SJA) comprises a housing defining an internal chamber. An orifice is present in a wall of the housing. The actuator further includes a mechanism in or about the housing for periodically changing the volume within the internal chamber so that a series of fluid vortices are generated and projected in an external environment out from the orifice of the housing. Various volume changing mechanisms are known, for example a piston positioned in the jet housing to move so that fluid is moved in and out of the orifice during reciprocation of the piston, or a flexible diaphragm as a wall of the housing. The flexible diaphragm is typically actuated by a piezoelectric actuator or other appropriate means.
A conventional SJA configuration is shown in
When voltage is not applied to the active diaphragm, the active diaphragm is substantially flat as shown in
In the past a few years, a number of computational fluid dynamics studies have indicated that SJAs have the potential to be used for active flow control in supersonic, hypersonic, and subsonic vehicles. A number of theoretical studies indicate that the synthetic jet actuator is one of the most efficient devices for flow control. According to these studies, the interaction of synthetic jets with an external cross flow over the surface on which they are mounted can displace the local streamlines and can induce an apparent or virtual change in the shape of the surface, thereby effecting flow changes on length scales that are one to two orders of magnitude larger than the characteristic scale of the jets. Global control of the aircraft will be enhanced, using this new-generation control structure. A number of experimental studies have demonstrated this effect, but they have shown that jet velocity is not high enough to be used at supersonic speeds. Unfortunately, the jet velocity and mass flow rate of currently existing SJAs are not high enough to meet the needs of active dynamic controls for space missions. In today's technological climate, there is a strong impetus to develop piezoelectric synthetic jet actuators with jet velocities of over 150 meters per second (m/s) at non-resonance working mode.
The advanced high performance vertical hybrid electroactive synthetic jet actuator (ASJA-V) is a synthetic jet actuator with three-dimensional active walls synergistically cooperating with each other, utilizing the positive and negative strains of the electroactive materials in different directions. The novel ASJA-V can provide active aerodynamic control for supersonic, hypersonic, and subsonic fixed wing aircraft and subsonic rotary wing aircraft.
In one embodiment of the invention, a synthetic jet actuator comprises an electroactive cylindrical wall, a first end electroactive diaphragm, and a second end electroactive diaphragm. The first and second end electroactive diaphragms are joined to the electroactive cylindrical wall at opposing ends of the electroactive cylindrical wall such that the formed chamber has a closed cylinder shape. The electroactive cylindrical wall defines the orifice therethrough. The orifice may have a generally frustoconical shape
The electroactive cylindrical wall may comprise multiple layers of electroactive material. The first and second end electroactive diaphragms each may comprise a layer of electroactive material bonded to a layer of metal. The electroactive material layer may comprise multiple concentric cylinders of electroactive material. The first and second end electroactive diaphragms are typically sized such that at least the electroactive material layer fits within the electroactive cylindrical wall. A flexible sealer is typically disposed between the electroactive material layer and the electroactive cylindrical wall.
The positive strain and negative strain of the electroactive cylindrical wall are typically configured such that, when voltage is applied to the electroactive cylindrical wall, (i) a height of the electroactive cylindrical wall decreases, (ii) a thickness of the electroactive cylindrical wall increases, (iii) an inner diameter of the electroactive cylindrical wall decreases, and (iv) a diameter of the orifice decreases. The positive strain or negative strain of the first and second end electroactive diaphragms are typically configured such that, when voltage is applied to the first and second end electroactive diaphragms, a potential increase in a diameter of each electroactive diaphragm is restricted by the electroactive cylindrical wall, thereby causing a center of each electroactive diaphragm to flex toward the other electroactive diaphragm. The flexing of the first and second end electroactive diaphragms toward each other may be further enhanced by the decrease of the inner diameter of the electroactive cylindrical wall.
Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.
Synthetic jet actuators of embodiments of the invention comprise a plurality of walls forming a chamber, where each of the plurality of walls comprises electroactive material. By having all of the walls comprise electroactive material, upon application of a voltage to all of the walls the size of the chamber is reduced in all three dimensions. This three-dimensional reduction in the size of the chamber causes a much greater reduction of reservoir volume as compared to conventional SJA. Embodiments of the invention will be described herein in which the synthetic jet actuators of embodiments of the invention have generally a closed cylinder shape (with the walls forming a chamber and at least one wall defining an orifice).
The deformations of the three electroactive walls of the ASJA-V are hybrid in order to obtain maximum changes of the jet reservoir volume and the diameter of the jet orifice. For each cycle, the change of reservoir volume of the ASJA-V is over five times greater than that of a conventional SJA (which has only one electroactive component—a negative strain-based bottom piezoelectric diaphragm). This much greater reservoir volume change provided by the novel structure of the present invention improves the mass flow rate so that it is many times greater than that of a conventional SJA. Simultaneously, the reduction of the orifice (inlet/outlet) diameter produces a higher jet velocity when the volume of the reservoir is actively reduced. The ASJA-V concept has a much higher performance than the conventional SJA because of the three-dimensional active motion of the device walls. Due to the physical structure and dimensions of the ASJA-V, the ASJA-V may be favorable for the case in which the height of the SJA is not critical.
The embodiment illustrated in
The first and second end electroactive diaphragms can be either a negative transverse strain based diaphragm (substantially the same as the diaphragm in the conventional SJA of
Referring now to
Referring now to
The multilayer electroactive layer 24 b, 26 b is formed with a plurality of concentric (nested), thin, short cylinders 40. Any desired number of layers or cylinders may be used. As illustrated in
The ASJA-V of embodiments of the invention can be used in broad areas of dynamic control. Each aircraft needs several dozen of this kind of device for local aerodynamic control. In addition, underwater facilities also need this kind of device for control and detection.
In one exemplary embodiment, an ASJA-V is constructed having physical dimensions as indicated in Table 1.
In order to optimize the design of the present ASJA-V, it is desirable to study the characteristics of the electromechanical response in electroactive ceramics/single crystals first as illustrated in
Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.